Elongated workpieces, for instance, bars or tubes having impermissible deviations in linearity, are customarily straightened in the course of manufacture by means of a continuously operating straightening machine, for instance, a roll straightener. However, the deflected ends to the workpieces are only partially, if at all, subject of this straightening process. In workpieces having cross sections at their ends which are different from the rest of the workpiece, as in, for instance, bulged or upset pipe ends, the previously known continuous method fails entirely. For this reason, such workpieces, which in accordance with their specifications or due to the requirements of the further processing are desired to have only limited deviation in linearity, are, therefore, subsequently straightened manually by means of gag presses. This method is expensive and requires a suitably trained operator having an accurate measuring eye. Furthermore, for the turning of the workpiece which is necessary during the straightening process, there must be present a suitable apparatus for handling the individual pieces, some of which are heavy, namely either a crane, hoist or the like.
From the Federal Republic of Germany 1901184, an apparatus is known for the dynamic balancing of workpieces which includes a driven crankshaft of adjustable eccentricity which is firmly connected via a crank arm to the workpiece. The workpiece is firmly supported at its ends and the axis of the workpiece is rotatingly deflected beyond the elastic limit of the workpiece at the place of clamping of the crank arm. The rotating deflection takes place in this connection without rotation of the workpiece around its own axis.
This apparatus has a disadvantage of the disproportionally high structural expense for varying the eccentricity of the crankshaft. Furthermore, the apparatus is not suitable for straightening the ends of elongated workpieces.
An object of the present invention is thus to provide a structurally simple apparatus with which the ends of elongated workpieces can be effectively straightened.
This object is achieved by providing an apparatus for straightening the end of an elongated workpiece having a longitudinal axis at a locus and an elastic limit, comprising means arranged symmetrically about the workpiece for deflecting the longitudinal axis of the workpiece for a predetermined amount and along a path of revolution around the locus without rotating the workpiece around the axis, the means comprising at least three load applying members arranged symmetrically around a common axis for selectively applying a predetermined load to the workpiece by moving perpendicular to the axis; actuator means connected to each load applying member for imparting load applying movement to the workpiece; and means connecting the actuator means for selectively controlling each actuator means so as to impart to the load applying members a phase shifted sinusoidal stroke movement. The movement of the load applying members is controlled responsive to time and path of the movement so that it results in a sinusoidal stroke movement.
The method according to the present invention comprises centering the workpiece between at least three load applying members which are disposed radially and symmetrically about the workpiece so that the longitudinal axis of the workpiece is positioned at a certain location. Thereafter, the longitudinal axis of the workpiece is deflected away from that location by applying a load with at least one of the load applying members in a predetermined amount and perpendicular to the axis and beyond the elastic limit of the workpiece. The load applying members of the apparatus are then controlled so that the deflected axis of the workpiece describes an imaginary path of revolution around the original location of the axis. In other words, the axis of the workpiece is deflected from an original first position or location, for a predetermined amount, to a second location. The workpiece is then acted upon by the load applying members in a manner so that the imaginary point of the second location describes a revolution about the first location of the axis of the workpiece. The predetermined maximum deflection is maintained over at least one revolution.
In the method of the invention, and with the workpiece kept stationary, at least one desired cross section of the workpiece in the region of the ends thereof is subjected to an increasing and decreasing alternate bending stress. In this operation the bending stress is selected so that the desired cross section of the workpiece is deformed up into the plastic region. A characteristic feature of the method of the present invention is that the maximum deflection resulting from the bending stress, which can be determined in advance as a function of the material used, moves one or more times around the axis of the workpiece. The straightening process itself can take place in various manners, depending on whether the maximum deflection is applied rapidly within a short time or only gradually. In the former case, after a centering of the workpiece, it is suddenly acted on so that the maximum amount of deflection is reached. This maximum point of deflection is then rotated one or more times around the original location of the axis of the workpiece. This is followed by a sudden release from the load. In the second case, the workpiece after the centering thereof, is acted on by a load to reach a given deflection which then rotates in the manner described, while the bending stress is continuously increased during the rotating of the deflection until the maximum deflection is reached. The latter is then maintained over a given path of rotation followed by continuous reduction in the bending stress until complete release of the workpiece from the load. The method of the present invention can be applied both to cold and heated workpieces.
The apparatus includes at least three and preferably four load applying members such as rams arranged symmetrically around a common axis, each of the rams being connected to a separate actuator such as a piston-cylinder unit. The piston and cylinder units are controllable with respect to path and time so that during the straightening process the respective pistons carry out a sinusoidal movement with respect to time. The controls of the piston-cylinder units are connected with each other so that they can operate out of phase with each other.
The advantage of the apparatus and method of the present invention resides in the fact that the workpiece is stationary during the straightening process and no rotating tool of expensive design is required. The method can be carried out automatically and can easily be integrated in a by-pass of a manufacturing line. By the use of suitably dimensioned hydraulic cylinders, the apparatus can be rapidly and easily adjusted without conversion to different dimensions of the workpiece. The desired maximum deflection can be selected freely, depending on the material used.